The invention relates to an air spring.
A known air spring for use between relatively-vibrating bodies has a gas-pressurized, variable interior space connected to a gas outlet valve and to a gas intake valve which, in turn, is connected to a compressed-gas reservoir. Each of the intake and outlet valves has a valve seat and a positioning element (hereafter called a stem) elastically pressed thereunto. At least one actuating piston actuates (opens and closes) not more than one of the two valves. For this, a face of the actuating piston is subjected to the gas pressure of the interior space and displaceable in a housing in the direction for actuating the valve, the seat of the other valve being formed by the housing.
For one example, German patent publication DAS No. 12 82 475 discloses a pneumatically-damped air-suspension system in which a double-acting valve connects the variable interior space of an air spring to an equalizing space. The valve is actuated by vibration-induced pressure differentials between the interior space of the air spring and the equalizing space to provide some compensation for the over- or under-pressures in the air spring producing the pressure differentials.
For another example, another air spring is described in U.S. Pat. No. 2,965,372. In it, the variable interior space for spring action between relatively-vibrating bodies is formed by one side of a double-ended piston and cylinder combination. The one side of the piston is acted on by compressed gas at a mean pressure, but when external, vibration forces change the variable interior space and, thus, its pressure, this displaces the piston and, thereby, actuates a valve which adjusts a gas pressure acting on the other, side of the piston to the gas pressure then effective on the one, first-mentioned side. This effectively-reciprocal adjustment of the gas pressures on both sides of the piston is effected by supplying gas at a pressure above the mean pressure from a surge tank or by exhausting gas to the atmosphere. However, the valve actuation is dependent on the instantaneous piston position and, thus, makes no allowance for the phase shift of the instantaneous gas pressure relative to the associated piston position which becomes significant when higher-frequency vibrations are introduced into the air spring. The valve actuation then is incorrect and results in poor isolating action.